The latest fracas surrounding Facebook's controversial new advertising platform involves MoveOn.org, the perhaps equally controversial civic action group best known for its strident calls to end the war in Iraq, including a full-page ad it bought in The New York Times: "General Petraeus or General Betray Us?"

MoveOn has charged that Facebook's Beacon advertising program, which allows participating advertisers to pair branded messages with users' profiles based on their activities on external sites, is a "huge invasion of privacy."

Facebook has now responded to MoveOn's charges.

"We encourage feedback from our users on new products, but in this case, the MoveOn.org-led group misrepresents how Facebook Beacon works," a Facebook spokesperson wrote in an e-mail to InternetNews.com.

"Beacon gives users an easy way to share relevant information from other sites with their friends on Facebook. Information is shared with a small selection of a user's trust network of friends, not publicly on the Web or with all Facebook users. Users are also given multiple ways to choose not to share information from a participating site, both on that site and on Facebook."

Beacon tracks the purchases Facebook members make on participating sites and incorporates that information into a mini-feed about that user's activities. Facebook claims that the activities that Beacon sends into the feeds do not reveal any personal information that could identify users.

MoveOn's answer: "If Facebook's argument is that sharing private information with hundreds or thousands of someone's closest 'friends' is not the same as making that information 'public,' that shows how weak Facebook's argument is," MoveOn.org spokesperson Adam Green wrote InternetNews.com in an e-mail. "Tell that to the person whose whole Christmas shopping list is revealed to everyone they know or to the employee whose boss sees every book and movie they order online."

Additionally, MoveOn has started a petition demanding that Facebook do more to protect its users' privacy, an effort that it's promoting in part through a group it created on Facebook called, "Petition: Facebook, stop invading my privacy!" More than 5,500 users have joined the group since its inception Tuesday.

In a statement, MoveOn claims that Facebook's privacy measures are insufficient. Those measures include the "no thanks" option users can click to prevent a purchase or other action from being added to their mini-feed.

Instead of the opt-out link that users must click each time they want to prevent a purchase from being added to their news feed, MoveOn's statement called for a more general, "opt-in" policy. MoveOn claims that the opt-out link is easy to miss, and that many Facebook users have unknowingly had their shopping activities revealed to their friends.

"When you buy a book or movie online  or make a political contributiondo you want that information automatically shared with the world on Facebook?" MoveOn asks on the petition page of its Web site.

It then closes with a conciliatory note: "A lot of us love Facebookit's helping to revolutionize the way we connect with each other. But they need to take privacy seriously."